Democratic and Republican candidates seeking support in the 2016 U.S. presidential campaign descended Saturday on the Iowa State Fair in Des Moines, hoping to impress thousands of fairgoers who use the annual event in the Midwestern farm state to show off prized livestock, crafts and cooking recipes.

Candidate Donald Trump, the real estate magnate and television personality leading a list of Republican hopefuls, arrived in his private helicopter.

Democratic front-runner Hillary Clinton, surrounded by security and staff, was mobbed by reporters as she arrived alongside Iowan and former U.S. Senator Tom Harkin, who had just endorsed her. She later sampled a pork chop before she and her entourage left the event. U.S. Senator Bernie Sanders of Vermont, another Democratic candidate, also was on hand.

The brash and outspoken Trump used the event to rip Clinton, calling her the "worst [U.S.] secretary of state in history." He also promised action on immigration issues that continue to roil the American public and the political establishment.

"You are gonna love me in terms of immigration and illegal immigration. We are building a wall, it's gonna be a wall that is not ... nobody is going through my wall," he said, referring to his controversial proposal to build a barricade along the U.S. border with Mexico.

He also called for increased defense spending, saying America must become "so tough and so strong and so smart that nobody will ever mess with us."

Friday fundraiser

On Friday, at a fundraiser in Clear Lake sponsored by county groups in northern Iowa, Clinton and Sanders took turns ridiculing their Republican opponents, while each insisting they were the most qualified to press for economic and social justice for all Americans.

"Now, we know that most of the attention these days is on a certain flamboyant [Republican] front-runner," Clinton said, referring to Trump. But she advised those in the sold-out arena not to ignore statements from other Republican hopefuls, including former Florida Governor Jeb Bush and U.S. Senator Marco Rubio of Florida.

"Don't let the circus distract you. If you look at their policies, most of the other candidates are just like Trump, without the pizazz or the hair," she said.

Sanders also garnered standing ovations from the crowd, estimated at more than 2,000. "Nobody will fight harder to end racism in America and to reform our broken criminal justice system," he said.

The two candidates who emerge from the Republican and Democratic party presidential nominating contests will face each other in the November 2016 national election. The winner will take over the White House in January 2017, assuming power from President Barack Obama, who is limited by the U.S. Constitution to two terms in office.

The first election-year contests are the party caucuses in Iowa, set for February 1.